I. FIELD OF THE INVENTION
This invention relates to rotary cone drill bits and a means to prevent drill cuttings from entering the bearings.
More particularly, this invention provides a drilled cuttings diverter or barrier in conjunction with a circumferential groove on the backface of the bit leg.
II. DESCRIPTION OF THE PRIOR ART
It has long been recognized in the drill bit industry that the longevity of sealed bearing rotary cone drill bits is greatly increased if debris is prevented from entering the bearings associated with each of the rotary cones rotatively retained on the legs of a drill bit. Drill bits used in carrying out rotary drilling are subject to destruction by erosion caused by the abrasive effect of the rock detritus entrained in the drilling fluid. Fluid circulation is employed primarily to circulate or flush the debris or formation cuttings from the well bore. In actual practice, mud and solids from the circulating fluid and from the earthen formations pack onto certain portions of the bit structure. This packed material flows or extrudes and moves relative to certain portions of the bit. Since great pressures are utilized in the drilling operations, the movement or flow of this packed material has adverse effects on the bit structure and, in particular, the seal cavity, the seal and bearings associated with each rotary cone of the bit.
U.S. Pat. No. 2,960,313 addresses the foregoing problem. A means is provided to mechanically deflect mud and cuttings from a path that normally results in wear and destruction of a roller cone bit. A deflecting post or pin is provided in the leg backface. The end of the pin is adjacent a cone backface; the pin serving to deflect detritus or debris as it invades the space between the cone backface and the leg backface. The pin is fixed in the leg backface and has an exposed cylindrical end that terminates in a flat surface, the flat surface paralleling the rotary cone backface.
The deflecting post, while being somewhat effective in intercepting the flow of debris, its circular shape can divert debris and fluid towards a seal cavity thus allowing some debris to enter this cavity.
U.S. Pat. No. 3,013,621 describes a means to deflect abrasive particles or cuttings from the space formed between a leg backface and a conical cutter. An overlay of hardened materials is welded to the leg backface at an angle to a radial plane from a journal center line. The abrasion resistant material metallurgically attached to the leg backface serves to scrape or divert debris away from the cone bearings to prevent the debris from entering and destroying the bearing during operation of the bit in a borehole.
This means of diverting the fluid and accumulated cuttings is somewhat ineffective because the space between the leg backface and the cutter backface is very restricted. Therefore, a minimal volume of drilling fluid can be circulated between the cone and the leg backface to flush away the abrasive drill cuttings. This allows intimate contact of the abrasive cuttings with the seal gland promoting premature seal and bearing failure.
U.S. Pat. No. 5,056,610, assigned to the same assignee as the present invention, describes a roller cutter bit having a drill cuttings diverter means to prevent packing and abrasion of the bearing seal gland. This diverter means consists of a burn plug positioned in the leg backface that is energized to force the plug into contact with the roller cone backface to wipe clean the face proximate the seal gland.
Although this system initially does remove the build-up of detritus at the seal gland area, the hard metal burn plug wears a circumferential groove in the cone backface proximate the seal fairly rapidly, exposing the seal to more abrasive cuttings, thereby accelerating seal wear. A significant amount of heat is generated by the plug wearing a groove in the cone, which at times deteriorates the seal.
The present invention has an advantage over the above prior art mechanisms in that the leg backface surface is a recessed circumferential groove instead of a flat surface. A hard abrasive resistant shale diverter pad is affixed fully across the leg backface groove at an angle that is approximately tangent to the seal gland outer diameter so that the outer edge of the pad angles into the direction of the rotation of the cone. The diverter pad wipes the accumulated detritus from the roller cone heel area and the adjacent circumferential groove in the leg backface allows a significantly more than normal volume of drilling fluid to continuously flush the seal gland area clean of cuttings and other detritus.